Field of the Invention
The present invention relates to a method of processing a wafer using a gas in a plasma state.
Description of the Related Art
Electronic devices, typically mobile phones and personal computers, incorporate, as indispensable components, device chips that have devices such as electronic circuits, etc. thereon. A device chip is manufactured by demarcating the face side of a wafer made of a semiconductor material such as silicon or the like into a plurality of areas with a plurality of projected dicing lines also known as streets, forming devices in the respective areas, and then dividing the wafer into device chips corresponding to the devices along the projected dicing lines.
In recent years, wafers with devices formed thereon have often been thinned by a grinding process or the like for the purpose of reducing the size and weight of device chips to be fabricated from the wafers. However, if a wafer is thinned by a grinding process, the flexural strength of device chips produced from the wafer is lowered on account of strains, hereinafter referred to as “processing strains,” caused by the grinding process which are left on the ground surface of the wafer. One solution is to remove processing strains from the wafer in a plasma etching process which uses a gas in a plasma state after the wafer has been ground (see, for example, Japanese Patent Laid-Open No. 2000-353676).
A plasma etching apparatus that is used to remove processing strains from ground wafers usually has a vacuum chamber that houses therein a pair of electrodes in the form of flat plates which are parallel to each other. With a ground wafer placed between the electrodes, the vacuum chamber is evacuated and depressurized, and while the vacuum chamber is being supplied with an etching gas, a high-frequency voltage is applied between the electrodes to bring the gas into a plasma state. The gas in the plasma state is caused to act on the ground surface of the wafer to remove processing strains from the wafer.